Multi-electrode system with vibrating electrodes

ABSTRACT

A multi-electrode system includes a fiber holder that holds at least one optical fiber, a plurality of electrodes arranged to generate a heated field to heat the at least one optical fiber, and a vibration mechanism that causes at least one of the electrodes from the plurality of electrodes to vibrate. The electrodes can be disposed in at least a partial vacuum. The system can be used for processing many types of fibers, such processing including, as examples, stripping, splicing, annealing, tapering, and so on. Corresponding fiber processing methods are also provided.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. non-provisional patentapplication Ser. No. 14/798,794, filed Jul. 14, 2015, entitledMulti-Electrode System with Vibrating Electrodes, which is acontinuation of U.S. non-provisional patent application Ser. No.14/276,684, filed May 13, 2014, now U.S. Pat. No. 9,086,539, issued onJul. 21, 2015, entitled Multi-Electrode System with VibratingElectrodes, which is a continuation application of U.S. non-provisionalpatent application Ser. No. 13/185,223, filed Jul. 18, 2011, now U.S.Pat. No. 8,721,196, issued on May 13, 2014, entitled Multi-ElectrodeSystem with Vibrating Electrodes, which is a continuation application ofU.S. non-provisional patent application Ser. No. 12/688,489, filed Jan.15, 2010, now U.S. Pat. No. 7,985,029, issued on Jul. 26, 2011, entitledMulti-Electrode System with Vibrating Electrodes, which is acontinuation-in-part application of U.S. non-provisional patentapplication Ser. No. 12/027,394 filed Feb. 7, 2008, now U.S. Pat. No.7,670,065, issued on Mar. 2, 2010, entitled Multi-Electrode System,which claimed priority under 35 U.S.C. §119(e) from commonly owned U.S.provisional patent application Ser. No. 60/976,859 filed Oct. 2, 2007,entitled Multi-Electrode System In A Vacuum, U.S. provisional patentapplication Ser. No. 60/953,803 filed Aug. 3, 2007, entitled Three-phaseArc for Fiber Splicing and Improved Fiber Stripping, and U.S.provisional patent application Ser. No. 60/888,691 filed Feb. 7, 2007,entitled Three-Phase Arc for Large Diameter Fiber Splicing and ImprovedFiber Stripping, the disclosure of each of which is incorporated hereinin its entirety by reference.

FIELD OF INTEREST

The present inventive concepts relate to the field of fiber optics, andmore particularly to systems and methods for splicing and strippingoptical fibers.

BACKGROUND

Optical fiber fusion splicers commonly employ an electrical discharge toheat the fibers sufficiently for them to be fused together. Thiselectrical discharge is known in the industry as an “arc”. However,according to some sources, a discharge of this current level is not atrue arc, but a coronal discharge that generates a hot plasma field.

Recently, arcs of the same type have been adapted for use in strippingcoatings from fibers and cleaning residual debris from mechanicallystripped fibers. In FIG. 1A, the arc 106 is formed between sharplypointed tips of a pair of electrodes 102, 104 to heat a fiber 110, wherethe electrodes 102, 104 are spaced 1 mm to 10 mm apart, as is known. Asshown in FIG. 1B, larger electrode spacing is required to generate anarc 126 for splicing multiple fibers at once (e.g., fiber ribbons), andfor larger diameter fibers 130. The optical design of some splicers canalso require the electrode spacing “gap” to be larger in order toprevent the electrodes 122, 124 from physically occluding the opticalfiber path.

The electrodes are commonly made of tungsten. Although, in some cases,cerium or thorium are alloyed with the tungsten. These elements lowerthe thermionic work function of the electrode, which causes electrons tomore readily leave the surface of the electrode. This allows thedischarge to be initiated with a lower initial voltage. Alternatively,an external source of ions can be provided to assist in initiating thearc (e.g., Ion Enhanced Cold Plasma technology by 3SAE Technology,Inc.). It is possible to provide a suitable arc with ordinary steelelectrodes and with no external ionization, but the repeatability of thearc characteristics is typically poor.

The voltage applied to the electrodes can be DC (typically inconjunction with smaller electrode spacing) or AC (which allows a largerspacing between the electrode tips—up to 10 mm or more). The voltagerequired to initiate the discharge is determined by Paschen's Law, whichrelates the breakdown voltage of a gap between electrodes to a (complexand non-linear) function of the gas present in the gap (e.g., typicallyordinary air), pressure, humidity, electrode shape, electrode material,and gap distance. Many of the parameters required to apply Paschen's Lawto this system are not known, so little quantitative theoreticalanalysis of splicer arcs has been done. Typically, the initiatingvoltage is determined experimentally to be in the range of 5 kV to 30kV.

Once the arc has been initiated, sustained ionization of the plasma inthe discharge requires a lower voltage than initially applied. Theimpedance (i.e., the ratio of applied voltage to current) of the plasmaas a circuit element is difficult to predict. Splicer arcs are suspectedto exhibit negative impedance at some frequencies and current levels.These characteristics make “constant voltage” operation of a splicer arcvery difficult to achieve. Therefore, most of such systems arecontrolled to provide a constant average current. This correlates in areasonably predictable way with the observed power delivered to thedischarge and the resulting temperature of the fibers.

It is useful to provide a means of varying the arc power delivered tothe fibers, in order to provide correct heating for different fibertypes, and to compensate for differing conditions. This can be done byaltering the current delivered to the sustained arc (with the controlcircuit mentioned above) or by pulsing the arc on and off.

Most common optical fibers are 80 μm to 125 μm in diameter (notincluding outer coatings), such as that shown in FIG. 1A. However, someapplications, such as high-power fiber lasers, require fibers up to 1 mmor more in diameter. Most fusion splicers will not accept fibers greaterthan 200 μm in diameter. Specialty splicers exist for Large DiameterFibers (LDF), with various maximum diameter capabilities, depending ondesign features.

Successful splicers for the larger end of the LDF (>600 μm) spectrumhave typically used resistive filament heating or laser heating ratherthan an arc. For these large fibers, the dielectric nature of the fibermaterial can cause an arc to curve around the fiber, rather thanenveloping the entire circumference of the fiber in the plasma field, asshown in FIG. 1B. This causes uneven heating of the fiber, withresulting poor splice quality.

Devices which use arcs to strip fibers can also suffer from unevenheating effects. These “arc strippers” typically place the fiber justoutside the plasma field (above or below), so that heat from the arccauses decomposition of the coating. This necessarily causes the fiberto be hotter on one side than the other. For most coatings, this is nota problem. However, some coatings have a relatively narrow temperaturewindow for effective removal and could benefit from more even heatdistribution.

SUMMARY OF INVENTION

Provided are systems and methods using multiple electrodes to generatearcs used for thermal processing of one or more optical fibers,including, but not limited to: splicing, annealing, diffusion,stripping, tapering, and ablation, or combinations thereof. Such systemsand methods can also be useful in other applications and contexts, suchas for making optical fiber couplings. Such multiple electrode systemsand methods can employ vibration of one or more of the multipleelectrodes to broaden the plasma field, while continuing to maintainsufficient power to perform the above functions.

In accordance the present invention, a multi-electrode system can be athree phase system configured to operate in ambient conditions, or in apartial or complete vacuum, with vibration or isolation of one or moreof the multiple electrodes. There are several benefits of such systemsand methods. For example, such systems and methods, when provided in apartial or complete vacuum, provide enhanced isothermic stability of theplasma field due to the elimination (or reduction) of convection.Compare to conventional systems and methods, where as heat from theplasma rises (at atmospheric pressure) a turbulent upward breeze iscreated that can disturb the plasma and alter the thermal balance of theplasma or slightly alter the location of the section of the fiber beingheated.

Also such systems and methods, when provided in a partial or completevacuum, provide enhanced isothermic range of the plasma field due to theelimination (or reduction) of convection. Compare to conventionalsystems and methods, where as heat from the plasma rises (at atmosphericpressure) it creates a turbulent upward breeze that can disturb the iontrail between the electrodes. This disruption will destabilize andextinguish a plasma in air that is otherwise completely stable in avacuum or partial vacuum. Since air is an insulator, the dielectricbetween the electrodes is substantially reduced in a vacuum or partialvacuum. This dielectric reduction allows for an arc to be initiated andmaintained at power levels far below what is achievable in air.

Also such systems and methods, when provided in a partial or completevacuum, provide reduced electrode oxidation. By reducing the oxygenlevels present during plasma generation the electrodes will deteriorateat a substantially slower rate.

Also such systems and methods, when provided in a partial or completevacuum, provide elimination of combustion. Some fiber coatings such asacrylate (the most common fiber coating) are combustible in air atatmospheric pressures and can burn if exposed to a standard arc. Whenthe same process is implemented in a vacuum or partial vacuum the lackof oxygen prevents combustion of the coating allowing it to be thermallyablated (a process similar to “burst technology”).

In accordance with one aspect of the present disclosure, provided is amulti-electrode system comprising: a fiber holder that holds at leastone optical fiber; a plurality of electrodes arranged to generate aheated field to heat the at least one optical fiber; and a vibrationmechanism that causes at least one of the electrodes from the pluralityof electrodes to vibrate.

The at least one optical fiber can be at least one large diameteroptical fiber having a diameter of at least about 125 microns.

The at least one optical fiber can be a plurality of optical fibers.

The vibration mechanism can broaden a width of the heated field to afull, half max of a Gaussian thermal profile.

In some cases, at least two of the plurality of electrodes can bevibrated.

In other cases, all of the plurality of electrodes can be vibrated.

The system can further comprise a controller that controls the electrodevibration effected by the vibration mechanism.

The vibration mechanism can be or include at least one piezo actuator.

The frequency of vibration of the vibration mechanism can more than 0 Hzbut not more than about 10 Hz.

The plurality of electrodes can be two electrodes.

The plurality of electrodes can be three electrodes.

The plurality of electrodes can be four electrodes.

The plurality of electrodes can generate plasma arcs between adjacentelectrodes and the heated field can be a heated plasma field.

The heated plasma field can be a substantially uniform heated plasmafield.

The substantially uniform heated plasma field can have a temperature ofat least about 65° C.

The substantially uniform heated field can generate a fiber surfacetemperature of at least about 1600° C.

The substantially uniform heated field can generate a fiber surfacetemperature of at least about 3000° C.

The substantially uniform heated field can generate a fiber surfacetemperature in the range of about 25° C. to about 900° C. for strippingoptical fibers.

The plurality of electrodes can be disposed in at least a partialvacuum.

The electrodes can be disposed in a 22″ to 24″ Hg gauge vacuum, 200 to150 torr absolute.

The partial vacuum can be an oxygen-enriched partial vacuum.

The distance between at least two of the plurality of electrodes can beadjustable.

In accordance with another aspect of the present invention, provided isa multi-electrode system that comprises: a fiber holder that holds atleast one optical fiber; a plurality of electrodes arranged to generatea substantially uniform heated plasma field to heat the at least oneoptical fiber; and a vibration mechanism that causes at least one of theelectrodes from the plurality of electrodes to vibrate, wherein thevibration mechanism broadens a width of the substantially uniform heatedplasma field to a full, half max of a Gaussian thermal profile.

In accordance with another aspect of the present invention, provided isa method of generating a heated field for processing at least oneoptical fiber. The method includes: holding the at least one opticalfiber in a fiber holder; using a plurality of electrodes, generating theheated field to heat the at least one optical fiber; and vibrating atleast one of the electrodes from the plurality of electrodes.

The at least one optical fiber can be at least one large diameteroptical fiber having a diameter of at least about 125 microns.

The at least one optical fiber can be a plurality of optical fibers.

Vibrating the at least one electrode can broaden a width of the heatedfield to a full, half max of a Gaussian thermal profile.

The heated field can be a substantially uniform heated plasma field.

The method can include disposing the plurality of electrodes in at leasta partial vacuum.

The plurality of electrodes can be two electrodes.

The plurality of electrodes can be three electrodes.

The plurality of electrodes can be four electrodes.

In some cases, the method can include vibrating at least two of theplurality of electrodes.

In other cases, the method can include vibrating all of the plurality ofelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing figures depict preferred embodiments by way of example, notby way of limitation. In the figures, like reference numerals refer tothe same or similar elements.

FIG. 1A and FIG. 1B are diagrams of a prior art dual electrodearrangement used for splicing an optical fiber, shown with a smalldiameter fiber in FIG. 1A and a large diameter fiber in FIG. 1B.

FIG. 2A is a diagram showing an embodiment of a multi-electrodearrangement in accordance with aspects of the present invention. FIG. 2Bis a block diagram showing an electrode support and fiber support thatcan be used with the embodiment of FIG. 2A. And FIG. 2C is an embodimentshowing a two electrode arrangement with vibrating electrodes.

FIG. 3 is a graph showing the relative sinusoidal phase of the threeelectrodes of the embodiments of FIGS. 2A and 2B.

FIG. 4 is a graph showing a preferred waveform for the current appliedto a set of transformer primaries to achieve the results in FIG. 3.

FIG. 5 is a schematic diagram of an embodiment of a circuit for drivingthe three electrode arrangement of FIGS. 2A and 2B.

FIG. 6A is a diagram showing another embodiment of a multi-electrodearrangement in accordance with aspects of the present invention.

FIG. 6B is a diagram showing a side view of the embodiment of FIG. 6A.

FIG. 6C is a plot showing a Gaussian thermal profile of the plasma fieldproduced by vibrating the electrodes in FIGS. 6A-B and 2A-B.

FIG. 7 is a schematic diagram of an embodiment of a circuit for drivingthree electrode arrangement of FIG. 6.

FIG. 8 is a flowchart depicting an embodiment of a real-time controlalgorithm 800 that can be implemented by the microcontroller unit ofFIG. 7.

FIGS. 9A and 9B are diagrams showing another embodiment of a threeelectrode arrangement in accordance with aspects of the presentinvention.

FIGS. 10A and 10B are diagrams showing another embodiment of a threeelectrode arrangement in accordance with aspects of the presentinvention.

FIGS. 11A-H show various embodiments of four electrode arrangements inaccordance with aspects of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

It will be understood that, although the terms first, second, etc. canbe used herein to describe various elements, these elements should notbe limited by these terms. These terms are used to distinguish oneelement from another, but not to imply a required sequence of elements.For example, a first element can be termed a second element, and,similarly, a second element can be termed a first element, withoutdeparting from the scope of the present invention. As used herein, theterm “and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that when an element is referred to as being “on”or “connected” or “coupled” to another element, it can be directly on orconnected or coupled to the other element or intervening elements can bepresent. In contrast, when an element is referred to as being “directlyon” or “directly connected” or “directly coupled” to another element,there are no intervening elements present. Other words used to describethe relationship between elements should be interpreted in a likefashion (e.g., “between” versus “directly between,” “adjacent” versus“directly adjacent,” etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a,” “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including,” when used herein, specifythe presence of stated features, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, steps, operations, elements, components, and/or groupsthereof.

In accordance with aspects of the present invention, provided is asystem having a multi-electrode arrangement configured for delivering asubstantially even distribution of heat about an optical fiber. As willbe appreciated by those skilled in the art, the techniques describedherein are applicable to providing arcs used for splicing and/orstripping optical fibers. Such multi-electrode systems can also beuseful in other contexts and applications, such as annealing, diffusion,tapering, and ablation. Such systems and methods can also be useful inother applications and contexts, such as for making optical fibercouplings. Generally, any of the foregoing, or combination thereof, canbe referred to as a multi-electrode system, a fiber preparation system,or a multi-electrode fiber preparation system.

In the illustrative embodiment of FIG. 2A a multi-electrode system 200comprises three electrodes 202, 204, and 206, which can be disposedaround at least one fiber 210. Here the electrodes are shown in a “Y”configuration, with a cross-sectional view of the fiber 210 shown. Thatis, fiber 210 would be extending out of the page, substantiallyperpendicular to the multi-electrode arrangement. While not shown, theat least one fiber 210 is held by a fiber holder (or support) such thatit can be disposed between the electrodes 202, 204, and 206. If the atleast partial vacuum is used, distal portions of the fiber(s) can exitthe vacuum enclosure through appropriate known sealing devices, ifdesired. Such fiber holders are known in the art.

In some embodiments, electrodes 202, 204, and 206 can also be disposedin at least a partial vacuum, as is shown by dashed line 220. In apartial vacuum of 22″ to 24″ Hg gauge vacuum (e.g., 200 to 150 torrabsolute), plasma temperatures as cool as 65° C. have been achieved.Room temperature plasmas are also possible at higher vacuum levels. Forsome fiber coatings, this process can be enhanced (e.g., better andfaster results) by stripping the fiber in an oxygen enriched partialvacuum with cool plasma (less than 400° C.). This approach etches thecoating off of the fiber, as opposed to a pyrolysis removal which canweaken the fiber and leave charring (i.e., carbon) at the interface ofthe strip window.

Regardless of whether or not the electrodes 202, 204, and 206 aredisposed in at least a partial vacuum, by placing three pointedelectrodes so their outputs form the vertices of an equilateral trianglearound the splice region within which at least one fiber can be located,it is possible to provide very evenly distributed heating around thecircumference of the fiber 210. By driving the three electrodes 202,204, and 206 with high-frequency (e.g., 30 kHz) AC voltages in a“three-phase” configuration, three separate arcs can be generated,referred to as arc 212, arc, 214, and arc 216 in FIG. 2A.

In the embodiment of FIG. 2A, the fiber 210 is completely surrounded bythe plasma arcs 212, 214, and 216, providing a heated plasma field 218having a very even heat distribution. It should be understood that asystem and/or method in accordance with aspects of the present inventionis capable of producing fiber surface temperatures like those producedby systems and methods using less than three electrodes, but does sowith improved uniformity. For example, a system according to aspects ofthe present invention can produce a plasma field sufficient to generatea fiber surface temperature in the range of about 25°-900° C. forstripping and up to about 1,600° C. or more for splicing. For example,temperatures in excess of 3,000° C. have been achieved. However, ifdictated by the physics of the fibers, fiber coatings, environmentalconditions, and/or other relevant parameters, the plasma field could begenerated to achieve other fiber surface temperatures.

The electrodes 202, 204, and 206 can be relatively close to the fiber210, which will expose the fiber directly to the plasma field 218.Alternatively, the electrodes 202, 204, and 206 can be further away,which would heat the fiber from the radiant heat of the plasma—this canbe more suitable for stripping/cleaning operations. In variousembodiments, the multi-electrode system can have a plurality ofsettings, e.g., 1 each for splicing and/or stripping a large fiber and asmall/standard fiber. In various embodiments, the multi-electrode system200 can be configured for adjusting the distance between the electrodes202, 204, and 206 within a range of positions. In various embodiments,the multi-electrode apparatus can be configured to detect the fiber sizeand self-position the electrodes 202, 204, and 206 as a function of thefiber size and the desired operation, e.g. splicing, annealing,diffusion, stripping, tapering, ablation, or making couplings. See, forexample, FIG. 2B.

For stripping some fiber coatings, direct exposure to the arc plasma isbeneficial, as an example. Ionized oxygen atoms within the plasma fieldoxidize and ablate the coating away. The electrode spacing can beconfigured to directly expose the coating surface to the plasma.Otherwise, the methods of using this effect are equivalent to those forstripping by thermal decomposition.

The electrodes 202, 204, and 206 can be placed in a “one down, two up”configuration as shown, or inverted, depending on the requirements ofother items near the fiber (such as the lenses of an optical system in asplicer). Alternatively, the electrodes 202, 204, and 206 can be placedin a horizontal plane, or irregularly spaced or angled according tovarious applications.

In this embodiment, the electrodes 202, 204, 206 are supported by (orattached to) an annulus 270, which can also be referred to as anelectrode support. Annulus 270 is coupled or attached to, or supportedby, a vibration mechanism 272. This arrangement is such, that vibrationmechanism 272 causes vibration of annulus 270, which in turn causes acorresponding vibration of electrodes 202, 204, 206. In this embodiment,annulus 270 defines an opening that enables easy fiber 210 loadingbetween the electrodes 202, 204, 206.

Vibrating electrodes 202, 204, 206 can have certain benefits, inparticular, broadening the width of the plasma field. Experimentation todate has shown that a Gaussian thermal profile along the axis of fiber210 is created when the electrodes are vibrated. Various aspects of thevibration are discussed in more detail with respect to FIGS. 6A-C.

The various techniques known for improving and controlling arcperformance with conventional two-electrode systems can also be appliedor adapted to embodiments, including pulse width modulation, ioninjection, feedback control, etc. The electrodes can also be fitted withshields or focusing sleeves or other technologies intended to alter arcdistribution. Known arc bending techniques utilizing dielectricsinserted near the plasma field can also be used.

The principles of the present invention could also be extended to asystem of four or more electrodes.

FIG. 2B shows an embodiment of an electrode support and fiber supportthat can be used with the system described above in FIG. 2A. Annulus270, as an electrode support, can be used to maintain the electrodes202, 204, 206 in their desired orientations about an axis on which theat least one fiber 210 can be disposed for splicing, annealing,diffusion, stripping, tapering, ablation, or for making optical fibercouplings. Vibration mechanism 272 (shown in FIG. 2A) can also be usedto selectively vibrate the annulus 270, or the electrode actuators 274could be used to vibrate one or more of electrodes 202, 204, 206. The atleast one optical fiber 210 is held and maintained in position by afiber support 234. Annulus 270 can include electrode actuators 274configured to adjust the distances of the electrodes 202, 204, and 206relative to the at least one optical fiber 210. Electrode actuators 274can also be configured to automatically adjust the distances of theelectrodes to the at least one optical fiber 210 as a function of adiameter of the at least one optical fiber, using, for example,piezoelectric actuators connected to a controller 230. Controller 230could include a microprocessor and memory that stores predefinedsettings for electrode configuration and/or distance from fiber as afunction of the size of the fiber and/or the processing to be done,e.g., splicing, annealing, diffusion, stripping, tapering, ablation, ormaking optical fiber couplings.

FIG. 2C is an embodiment showing a two electrode arrangement in at leasta partial vacuum, such as that described herein. That is, such electrodearrangements can also benefit from operation in such a vacuum, inaccordance with aspects of the present invention. In at least a partialvacuum, two electrodes can also achieve a plasma field having asubstantially even heat distribution. Additionally, one or more of theelectrodes 102, 104 can be coupled to a vibration mechanisms 103, 105,e.g., to create a broader plasma field. Vibration mechanisms 103 and 105can be the mechanism, two vibration mechanisms under common control bycontroller 230, or two vibration mechanisms independently controlled.

FIG. 3 is a graph 300 that shows an example of voltages which could beprovided at the electrodes 202, 204, and 206 to create a three-phasearc, as shown in FIG. 2A. The example shown has an overall frequency ofapproximately 22 kHz with a peak-to-peak voltage of 20 kV. Plot 312 isfor electrode 202, plot 314 is for electrode 204, and plot 316 is forelectrode 206.

In the example, there is an arc present between electrodes 204 and 206at time 0 μs, see plots 314 and 316. At approximately 6 μs, the arcshifts to the space between electrodes 202 and 206, see plots 312 and316. At 13 μs, the arc moves to electrodes 312 and 314, see plots 312and 314, and so forth. At any given time, an arc should be presentbetween two electrodes with the greatest potential difference betweenthem. The rotating phase sequence takes place so rapidly that the arcappears to be constantly on, and substantially constant heating isprovided, as the thermal time constants of the fiber and surrounding airare substantially longer than the oscillation period of the arc.

As noted in the background information, it is extremely difficult toactually control the voltage at the electrodes. However, the far morepractical method of controlling current to the primary of the step-uptransformer can be applied in the illustrative embodiment. FIG. 4 showsgraph 400 having a preferred waveform for the current applied to thetransformer primaries. This system of drive currents will produce outputvoltage waveforms roughly corresponding to those shown in FIG. 3,producing a controllable three-phase arc.

The primary drive currents for the transformers require three waveformsdisposed at 0 degrees phase, 120 degrees phase, and 240 degrees phase.These can be generated by well-known digital or analog means, such as aring counter. In graph 400, plot 412 is for electrode 202, plot 414 isfor electrode 204, and plot 416 is for electrode 206.

FIG. 5 is schematic diagram of an embodiment of a circuit 500 configuredto drive the three electrode 202, 204, and 206 arrangement of FIG. 2A.Six D-type flip-flops D1-D6 are configured to implement a circular shiftregister. A short startup pulse 502 is applied to initialize the circuit500. Initially, electrode 202 is positive and electrode 204 is negative,but then each sequences through the various phase states. As an example,the overall frequency can be ⅙ of the clock frequency of 132 KHz in thisembodiment. In other embodiments, this can differ, preferablymaintaining a substantially uniformly or evenly heated plasma field.Current control circuitry (not shown) can be substituted for the CD4050buffers 510, 512, 514, 516, 518, and 520.

The required voltages could be generated from three separate 10CT:780high voltage transformers 522, 524, and 526, or from a tuned LCconfiguration wound on a single core. It is also possible for the threetransformer 522, 524, and 526 secondaries to be connected in a “delta”configuration, wherein the secondary coils are connected betweenadjacent pairs of electrodes, rather than being referenced to ground asin FIG. 5.

In FIG. 5, MOSFETS 530, 532, 534, 536, 538, and 540 drive transformers522, 524, and 526. In accordance with various aspects of the invention,the multi-electrode system can include a dead-band feature to increasesefficiency and reduce dissipation in the drive transistors/MOSFETs 530,532, 534, 536, 538, and 540, by preventing overlap in conduction betweenthe “positive-driving” and “negative-driving” devices. The dead-bandfeature can also provide a mechanism for adjusting arc power (e.g., byvarying the width of the dead-band). The dead-band feature can alsoenable cleaner transitions between states of the arcs, by allowing anexisting arc to extinguish momentarily before establishing the next arcin the phase sequence.

The dead-band feature can be implemented by producing the controlledcurrent waveforms to include two dead-bands of 1% to 49% of the periodof the cycle, wherein there is substantially no current flow through thetransformer primary.

Another embodiment of a three electrode system can generate an arc ofsubstantially the same properties as that of the three electrode systemdescribed above with respect to FIG. 2A, but with one grounded electrodeand only two powered electrodes.

FIG. 6A shows an illustrative embodiment of a multi-electrode system 600having one electrode grounded and two electrodes powered, which can alsobe disposed in at least a partial vacuum 620. In such a case,corresponding benefits are possible with the embodiment of FIG. 6A asthose described above with respect to the embodiment of FIG. 2A. Here,electrodes 602, 604, 606 are used to generate arcs 612, 614, 616, whichin turn creates plasma field 618 around at least one fiber 610 disposedbetween the electrodes.

In a three-phase arc system 200 as described in with respect to FIG. 2A,electrodes 204, 204, and 206 are each driven by a voltage waveform,where the three voltage waveforms were 120° apart in phase. Thisproduces arcs 212, 214, and 216. In this embodiment, electrodes 602 and604 are oriented on a common axis, to form a “T” configuration withelectrode 606. The performance is substantially the same as if theelectrodes where oriented at 120° apart from each other, as in theembodiment of FIG. 2A. For this embodiment, however, the configurationis more compact, e.g., more suitable to be integrated into a fusionsplicer, without compromising performance. Those skilled on the art, nowhaving the benefit of this disclosure, will appreciate that otherelectrode orientations could be used.

In the present embodiment of FIG. 6A, electrode 606 is grounded. Ifelectrode 602 and electrode 604 are each driven by an identicalwaveform, at 0° relative phase, arc 612 would not be formed, as therewould be no potential difference between electrodes 602 and 604. Twoequal arcs will be formed, that is arcs 614 and 616, forming a “V”shape.

If electrode 606 remains grounded, and electrodes 602 and 604 are drivenby voltage waveforms of opposite polarity (i.e., 180° relative phase),only arc 612 will form. This is because the potential difference betweenelectrodes 602 and 604 is twice as great as the potential between eitherone of electrodes 602 and 604 and the grounded electrode 606.

Considering the above cases, it seems logical that at some particulardegree of phase separation (between 0° and 180°) between the voltagewaveforms applied to electrodes 602 and 604, with electrode 606grounded, that all three arcs 612, 614, 616 would be formed atsubstantially equal intensity. A theoretical analysis (based on vectormathematics) suggests that this would occur at 60° relative phase. Inimplementation, it has been found necessary to vary the phase betweenapproximately 40° and 160°, depending on various implementation factors,such as the frequency and power of the drive waveforms and the spacingand condition of the electrodes. In forming arcs 612, 614, and 616 atsubstantially equal intensity, a substantially uniform heated plasmafield 618 is generated around the at least one optical fiber 610.

In this embodiment, electrodes 602, 604, 606 are supported, coupled, ormounted to an annulus 670, like annulus 270 of FIG. 2A. Annulus 670 iscoupled or attached to, or supported by, a vibration mechanism 672, likevibration mechanism 272. The annulus can be made of any of a variety ofmaterials that maintain structural integrity within anticipated heatranges, such as ceramics.

FIG. 6B is a diagram showing a side view of the multi-electrode system600 of FIG. 6A. In this embodiment, annulus 670 is support on vibrationmechanism 672. Vibration mechanism 672 is arranged to cause annulus 670to vibrate back and forth within a range or distance Ad. Electrodes 602,604, 606 experience a corresponding vibration, which broadens the plasmafield 618 caused by arcs 612, 614, 616. As a result, the width of theplasma field 618 can be modulated.

The vibration mechanism can be any of a variety of types of vibrationmechanism, such as, for example, a piezo actuator that experiencesoscillation in the form of expansion and contraction in response to anapplied AC voltage. In the present embodiment, the piezo actuator can bemade of a crystal, ceramic, or other piezo material, or combinationsthereof. The piezo can be built into a flexure stage to provideprecision linear motion.

FIG. 6C shows two thermal profiles of a plasma field as Gaussian curves,for illustrative purposes. Here, the Y-axis represents Temperature andthe X-axis represents Distance from the electrodes with the center ofthe curve indicating a distance of 0. The first, narrow, thermal profileof the plasma field is indicated by the solid line, and is produced whenelectrodes are not vibrated. The second, wider, thermal profile of theplasma field is indicated by the dashed line, and is produced whenelectrodes are vibrated. For example, referring to the embodiment ofFIG. 6A the thermal profile of the plasma field 618 along the axis offiber 610 is significantly broader than it would be if none of theelectrodes 602, 604, 606 were not vibrated. Vibrating electrodes resultsin the broader thermal profile of the plasma field; power is alsopreferably added to maintain the plasma field at the Max value of thenon-vibrated electrode embodiments. The present invention is not limitedto the profiles shown in FIG. 6C, since these can be altered byadjustments in power, vibration frequency, and vibration range.

FIG. 7 is a schematic diagram of an embodiment of a circuit 700 fordriving the three electrode 600 arrangement of FIG. 6. The embodiment inFIG. 7 is similar to that of FIG. 5 in terms of buffers, MOSFETs andtransformers, but unlike FIG. 5, in FIG. 7 the third electrode is tiedto ground and does not include the buffer, MOSFET, and transformercircuitry.

In the embodiment of FIG. 7, the signals which turn the drive MOSFETs732, 734, 736, and 738 on and off can be generated by a programmablemicrocontroller unit 750, and provided via buffers 710, 712, 714, and716. As examples, the MOSFET drivers 732, 734, 736, and 738 can beMC34151 (or similar) MOSFETs and the microcontroller 750 can be aPAL18F2520 manufactured by Microchip, Inc. This circuit of thisembodiment allows real-time control and adjustment of the duration andphase relationship of the drive signals. The real-time adjustments canbe made with the goal of maintaining arcs 612, 614, and 616substantially equal in intensity or to deliberately alter their relativeintensity for various purposes.

In order for the microcontroller 750 to be able to sense the arcintensities, small-value resistors R1 (for example, 100 Ohm resistors)can be connected in series with the ground return of each drive signal.A voltage develops across the resistor R1 in direct proportion to thearc current delivered by the electrode 602. A sense resistor R1 isprovided for each electrode. For example, a 20 mA current from electrode602 would result in a 2V signal across the 100 Ohm sense resistor R1.

The sense resistor signals are in the form of high-frequency ACvoltages. It is possible to rectify and filter these signals to produceDC voltages, which are more suitable for measurement by themicrocontroller unit 750.

The simple rectification/filtering networks shown include a diode D, tworesistors R2 and R3, and a capacitor C, and are provided for each of thethree electrodes. This network produces a voltage proportional to thearithmetic mean (i.e., average) of the absolute value of the senseresistor voltage. If greater accuracy is required, well-known means canbe used to produce a voltage proportional to the quadratic mean (e.g.,root-mean-square or RMS) of the sense resistor voltage. The RMS value isa better measurement of the power delivered into the arc, which may beimportant in some applications.

An additional improvement to the embodiment can be to make the powersupply adjustable, which is shown as “12V” in FIG. 7. An adjustable“buck regulator” circuit, well-known in the art, can adjust the voltagedownward from 12V to a very low voltage (e.g. 1V) or any desiredintermediate voltage. This can be useful when an arc of very low poweris required, as it has been found that very low pulse widths to theMOSFET's (the previous method of obtaining low power operation) canresult in unstable arc operation. Alternatively, a lower input voltageand/or lower transformer step-up ratio can be used in conjunction with aboost-type regulator to provide an equivalent range of voltages.

FIG. 8 is a flowchart depicting an embodiment of a real-time controlalgorithm 800 that can be implemented by the microcontroller unit 750 ofFIG. 7. The control algorithm 800 performs an evaluation of sensedcurrents for each of electrodes 602, 604, and 606, represented ascurrents I₁, I₂, and I₃ in FIGS. 7 and 8. In this method the pulse widthof electrodes 602, 604, and 606 is adjusted based on whether the sensedcurrents I₁, I₂, and I₃ are substantially equal to a current I_(set)representing an initial current setting by microcontroller unit.

Specifically, in step 802 initial circuit settings are entered forelectrodes 602, 604, and 606, including initial current I_(set). In step804 a determination is made of whether I₁=I₂. If the answer is “yes,”then the method continues to step 810. If in step 804, I₁<I₂ then theprocess continues to step 806 where the pulse width for electrode 602 isincreased. If in step 804, I₁>I₂ then the process continues to step 808where the pulse width for electrode 604 is increased. As with step 804,after steps 806, 808 the process continues 810.

In step 810, a determination is made of whether I₃=I₁, I₂. If the answeris “yes,” the process continues to step 816. If in step 810, I₃>I₁, I₂then the process continues to step 812 where the phase difference isincreased. If in step 810, I₃<I₁, I₂ then the process continues to step812 where the phase difference is decreased. As with step 810, aftersteps 812, 814 the process continues to step 816, where a determinationis made of whether I₁, I₂, I₃=I_(set). If the answer is “yes,” then theprocess continues to step 804 and is repeated. If in step 816 I₁, I₂,I₃>I₃<I_(set) then in step 818 the pulse width for electrodes 602 and604 is decreased. If in step 816 I₁, I₂, I₃<I_(set) then in step 820 thepulse width for electrodes 602 and 604 is increased. In each case, theprocess then continues to step 804 and is repeated.

It will be apparent that there are other possible arrangements of theelectrodes that are within the spirit and scope of the invention. Thesealternative arrangements may be preferable in circumstances where it isdesired to change the pattern of heating of the fiber, or where analternative arrangement facilitates the positioning of the electrodeswith respect to other equipment in a larger system.

FIG. 9A (bottom view) and 9B (side view) are diagrams showing anotherembodiment of an electrode arrangement in accordance with aspects of thepresent invention. In these figures a three electrode fiber system 900is shown that includes electrodes 902, 904, and 906 placed in ahorizontal plane, so that the arcs 912, 914, and 916 are produced inthis same plane. The fiber 910 is disposed above this plane, so that itis heated substantially by an upward convective flow of heat from thearc region. The range of the distance between the planes in thisembodiment would be 1 mm-10 mm. The electrodes may be disposed in a “Y”configuration, “T” configuration, or such other configuration as theapplication requires or as may be convenient. For example, fourelectrodes could be placed to form a rectangular arc array, or fivemight be arranged in a pentagon shape. One or more of the electrodes902, 904, 906 may be coupled to a vibration mechanism 903, 905, 907—asdiscussed above.

FIGS. 10A (bottom view) and 10B (side view) are diagrams showing yetanother embodiment of a three electrode arrangement in accordance withaspects of the present invention. In these figures a three electrodefiber system 1000 is shown that includes electrodes 1002, 1004, and1006, which produce arcs 1012, 1014, and 1016. A fiber 1010 may bedisposed in the same plane (for example, a vertical plane) as theelectrodes 1002, 1004, and 1006. In this arrangement, the fiber 1010intersects at least two of the arcs 1012, 1014, and 1016. In this way,the fiber will be heated along a greater portion of its length, althoughthe circumferential heat distribution is not as even as in otherembodiments. One or more of the electrodes 902, 904, 906 may be coupledto a vibration mechanism 903, 905, 907—as discussed above.

FIGS. 11A-H show various embodiments of a multi-electrode system 1110that uses four electrode arrangements in accordance with aspects of thepresent invention. In each embodiment, electrodes 1102, 1104, 1106, and1108 are shown, and create arcs 1112, 1114, 1116, and 1118. The arcscreate a plasma field 1119, which heats at least one fiber 1110. Theelectrodes may be disposed in at least a partial vacuum 1120, asdiscussed above, but embodiments without the at least partial vacuum1120 also may be used. One or more of electrodes 1102, 1104, 1106, and1108 can optionally be mounted to a vibration mechanism 1172, asdiscussed above. Other embodiments can forego one or both of thevibration mechanism and at least partial vacuum.

In FIG. 11A the fiber 1110 is oriented orthogonally with respect to theelectrodes and in FIG. 11B the fiber 1110 is oriented in parallel withthe electrodes. In FIG. 11C the electrodes are oriented in a cross (“X”)arrangement. In FIG. 11D the electrodes are arranged diagonally withrespect to the fiber 1110. In FIG. 11E pairs of electrodes are orientedin different planes and the fiber is oriented in a third plane thatpasses between the planes within which the electrodes are oriented. Inthe embodiments of FIGS. 11A-D, the electrodes can all be in the sameplane. In the embodiments of FIGS. 11A-C, the fiber may be in the sameplane as the electrodes or proximate to the plane of the electrodes.

In any of the embodiments shown in FIGS. 11A-11E, fiber 1110 could bearranged as if it were coming out of the page, e.g., substantiallyperpendicular to the page and field 1119. As an example, FIG. 11F showsthe embodiment of FIG. 11C where fiber 1110 is coming out of the page.FIG. 11G shows the embodiment of FIG. 11A or 11B where fiber 1110 iscoming out of the page. And FIG. 11H shows the embodiment whereelectrodes 1102 and 1104 are aligned and electrodes 1106 and 1108 areangled, and fiber 1110 is coming out of the page. The embodiment of FIG.11H could also be used with fiber 1110 crossing arcs 1112 and 1116, 1114and 1118, or in some other arrangement.

These are only examples of possible alternative arrangements of theelectrodes and fiber. The present invention lends itself to a widevariety of arrangements, due to its unique capability of maintaining aplurality of controlled arc discharges. In any of the three electrodeembodiments, the circuit of FIG. 5 or 7 could be used to drive suchelectrodes.

While the foregoing has described what are considered to be the bestmode and/or other preferred embodiments, it is understood that variousmodifications can be made therein and that the invention or inventionscan be implemented in various forms and embodiments, and that they canbe applied in numerous applications, only some of which have beendescribed herein. It is intended by the following claims to claim thatwhich is literally described and all equivalents thereto, including allmodifications and variations that fall within the scope of each claim.

What is claimed is:
 1. A multi-electrode system comprises: at least oneoptical fiber holder configured to hold at least one optical fiber; aplurality of electrodes arranged around the at least one optical fiber;and a control circuit electrically coupled to the plurality ofelectrodes and configured to drive the plurality of electrodes in arotating phase sequence to generate at least one arc that pulses on andoff to form a substantially uniform heated field to provide evenlydistributed heating around a circumference of the at least one opticalfiber, wherein the rotating phase sequence takes place so rapidly thatsubstantially constant heating is provided to the at least one opticalfiber, as thermal time constants of the at least one optical fiber andsurrounding air are longer than an oscillation period of the at leastone arc.
 2. The system of claim 1, wherein one or more of the pluralityof electrodes are coupled to a vibration mechanism configured to vibratethe one or more electrodes.
 3. The system of claim 2, wherein thesubstantially uniform heated field has a first width when the one ormore electrodes are not vibrated and a broader width when the one ormore electrodes are vibrated.
 4. The system of claim 1, wherein two ormore of the plurality of electrodes are coupled to two or more vibrationmechanisms configured to vibrate the two or more electrodes.
 5. Thesystem of claim 4, wherein the two or more vibration mechanisms arecommonly controlled by a controller.
 6. The system of claim 4, whereinthe two or more vibration mechanisms are independently controlled. 7.The system of claim 1, wherein one of the plurality of electrodes isgrounded and at least one other of the plurality of electrodes is drivenby an AC voltage and/or current.
 8. The system of claim 1, wherein theplurality of electrodes is 2 electrodes.
 9. The system of claim 1,wherein the plurality of electrodes is 3 electrodes.
 10. The system ofclaim 1, wherein the plurality of electrodes is 4 electrodes.
 11. Thesystem of claim 1, wherein the at least one optical fiber has a diameterin a range of between about 80 μm to about 200 μm.
 12. The system ofclaim 1, wherein the at least one optical fiber has a diameter in arange of about 200 μm to about 600 μm.
 13. The system of claim 1,further comprising: a vacuum chamber configured to maintain at least apartial vacuum, wherein the at least one optical fiber holder configuredto hold at least one optical fiber and the plurality of electrodes aredisposed within the vacuum chamber.
 14. The system of claim 1, whereinthe heated field is a heated plasma field generated by the plurality ofelectrodes.
 15. The system of claim 1, further comprising: one or moreelectrode actuators configured to automatically adjust the distances ofone or more of the electrodes to the at least one optical fiber as afunction of a diameter of the at least one optical fiber.
 16. Amulti-electrode system comprises: at least one optical fiber holderconfigured to hold at least one optical fiber; a plurality of electrodesarranged around the at least one optical fiber; at least one vibrationmechanism coupled to one or more of the plurality of electrodes; and acontrol circuit electrically coupled to the plurality of electrodes andthe at least one vibration mechanism, the control circuit configured to:drive the plurality of electrodes in a rotating phase sequence togenerate at least one arc that pulses on and off to form a substantiallyuniform heated plasma field, and drive the at least one vibrationmechanism to vibrate one or more of the plurality of electrodes tobroaden the width of the substantially uniform heated plasma fieldaround the at least one optical fiber to form a broadened substantiallyuniform heated plasma field around a circumference of the at least oneoptical fiber, wherein thermal time constants of the at least oneoptical fiber and surrounding air are longer than an oscillation periodof the at least one are generated by the rotating phase sequence of theplurality of electrodes.
 17. The system of claim 16, further comprising:a vacuum chamber configured to maintain at least a partial vacuum,wherein the at least one optical fiber holder configured to hold atleast one optical fiber and the plurality of electrodes are disposedwithin the vacuum chamber.
 18. The system of claim 16, wherein theplurality of electrodes is 2 electrodes.
 19. The system of claim 16,wherein the plurality of electrodes is 3 electrodes.
 20. The system ofclaim 16, wherein the at least one optical fiber has a diameter in arange of about 200 μm to about 600 μm.